Pusher arm and ball release mechanism for embolic coils

ABSTRACT

This disclosure concerns release mechanisms for medical implants, particularly embolic coils and the like, which utilize bulbous elements and receiving elements to constrain the bulbous elements. In some cases, the receiving elements are sized and shaped to help constrain the bulbous element axially and/or radially, and may work in concert with constraining elements and/or release wires that are optionally moveable independently of the receiving elements.

PRIORITY

This application claims the benefit of priority under 35 U.S.C. § 119 toU.S. Provisional Patent Application Ser. No. 62/237,904, filed Oct. 6,2015, which is incorporated by reference in its entirety and for allpurposes.

FIELD OF THE INVENTION

This application relates to the field of medical devices and medicalprocedures. More particularly, the application is related to devices andmethods for occluding body lumens such as blood vessels.

BACKGROUND

Therapeutic embolization or occlusion of blood vessels may be used totreat a variety of vascular and non-vascular conditions includingcerebral and peripheral aneurysms, arteriovenous malformation, uterinefibroids and various tumors. One commonly used agent for embolizingblood vessels is the embolic coil, a permanently implanted coiled wirestructure which, when implanted into a blood vessel, occludes the vesselby causing thrombosis where it is deployed. Embolic coils may havedifferent lengths and/or cross-sectional diameters, in order to fit intoand occlude vascular structures of varying sizes. In use, the coils aredelivered through a microcatheter in a narrow-diameter elongatedconfiguration (e.g. to fit within a 3 Fr catheter lumen). Once deployedinto the vessel, the coil may assume a complex 3-D shape such as ahelix, a spiral, a J-shape, or a birds-nest shape, and may includethrombogenic fibers or bundles of fibers along its length. Embolic coilsare highly flexible, and can be delivered through narrow or tortuousvascular structures, but when occlusion of relatively large vascularstructures is desired, multiple coils may be necessary to achieve fullocclusion.

These coils have typically been placed at the desired site using acatheter and a pusher. The site is first accessed by the catheter. Intreating peripheral or neural conditions requiring occlusion, the sitesare accessed with flexible, small diameter catheters, which may beguided to the site through the use of guidewires and/or flow-directedmeans such as balloons at the distal end of the catheter. Once the sitehas been accessed, the catheter lumen is cleared (i.e., the guidewire isremoved if a guidewire has been used), and the coil is placed in theproximal end of the catheter and advanced through the catheter with apusher. When the coil reaches the distal end of the catheter it isadvanced into the vessel and deployed. This technique of plunging thecoil from the distal end of the catheter has undesirable limitations.First, because of the plunging action of the pusher during deployment,the positioning of the coil at the site cannot be controlled to a finedegree of accuracy. Second, once plunged from the catheter, it isdifficult to reposition or retrieve the coil if desired. Indeed, anotherdevice, called a retriever, must be threaded through the catheter tosnare the coil to reposition or retrieve it.

The coil is typically connected to the pusher or another structurewithin the catheter and must be detached. This detachment is typicallyfacilitated by the use of an electrolytically severable link or amechanical coupling. While current detachment mechanisms are generallyreliable, they may not release the coil when triggered 100% of the time.In the case of mechanical detachment mechanisms in particular, improvingdetachment reliability may involve undesirable trade-offs such asincreasing the size and/or cost of parts used in detachment mechanisms.

SUMMARY OF THE INVENTION

The present invention, in its various aspects, provides improvedmechanical coil detach systems which achieve 100% detachment and whichminimize the trade-offs between 100% detachment and increased sizeand/or expense.

In one aspect, the present invention relates to a system for treating apatient which includes a catheter defining a lumen, a pusher assemblyslidably disposed within the lumen, a constraining element slidablydisposed within the lumen and moveable independently of the pusherassembly, which constraining element has a tubular distal end disposableabout a distal portion of the pusher assembly, and an embolic coil witha proximal end comprising a bulbous element. The pusher assembly, inpreferred embodiments, includes a distal receiving element having afirst portion defining a first planar surface extending radially and asecond portion defining an elongated planar surface extendingsubstantially perpendicular to and distally from the planar surface, theelongated planar surface having a protrusion extending away from theplanar surface. In some embodiments, the inner diameter of the tubulardistal end of the constraining element is closely toleranced to thecombined outer diameter of the bulbous element of the embolic coil andthe second portion of the distal receiving element (for instance, theinner diameter is, in some cases, not more than 133% of (a) an outerdiameter of the bulbous element of the embolic coil, plus (b) athickness of the second portion of the distal receiving element).Similarly, in some embodiments, the protrusion extends a distance fromthe elongated planar surface that is less than 50% of a diameter of thebulbous element. More generally, in certain embodiments, the combination(i.e. the combined thickness) of the extension of the protrusion fromthe elongated planar surface and the second portion of the distalreceiving element is greater than or equal to a difference between theinner diameter of the tubular distal end of the constraining element andthe combined outer diameter of the bulbous element of the embolic coiland the second portion of the distal receiving element. In some cases,the bulbous element is connected to the embolic coil by one of a wireand a rod extending axially along a central axis of the coil, andwherein the wire or rod extends axially along a central axis of theembolic coil when the bulbous element and receiving element are engagedand disposed within the lumen of the tubular distal end of theconstraining element. The constraining element and pusher assembly maybe arranged within the lumen in several different ways to permit smoothcatheter operation and/or to minimize the potential for mechanicalinterference between those parts. For instance, in some cases theconstraining element includes a wire or a rod disposed proximally of thetubular distal end, the wire or rod extending parallel to the pusherassembly, in which case the pusher assembly is disposed coaxially withinthe catheter lumen. In other cases, the constraining element includes acoiled segment disposed proximally of the tubular distal end, in whichcase the pusher assembly is disposed coaxially within a lumen defined bythe coiled segment. In still other cases, the constraining elementincludes a wire or a rod disposed proximally of the tubular distal endand disposed coaxially within the catheter lumen and the pusher assemblyincludes an elongated portion extending parallel to the wire and througha proximal aperture within the tubular distal end. In various cases, thedistal receiving element is a single piece. In preferred cases, theembolic coil is secured to the catheter by contacting the bulbouselement and the distal receiving element and advancing the constrainingelement at least partially over the bulbous element and the distalreceiving element and, optionally, the coil is released by moving atleast one of the pusher assembly and the constraining element relativeto the other. In some cases, the pusher assembly and constrainingelement can be retracted from the catheter and replaced with a pusherassembly and constraining element engaged with a second embolic coil.The system according to this aspect can be used in medicine, forinstance for the treatment of vascular conditions, and can be includedin kits for use by medical personnel.

In another aspect, the present invention relates to a system fortreating a patient which includes a catheter defining a first lumen, apusher assembly slidably disposed within the first lumen and having atubular distal element defining a second lumen, which tubular distalelement includes a slot formed in a wall thereof, a release wireslidably disposed within the first lumen and moveable independently ofthe pusher assembly, and an embolic coil with a proximal end comprisinga bulbous element. In various embodiments according to this aspect, thetubular distal end has an inner diameter that is less than a combineddiameter of the bulbous element plus a diameter of the release wire, andwherein the release wire is disposable (i.e. it can be positioned) nearan inner wall of the tubular distal element opposite the slot so as todisplace the bulbous element into the slot. The pusher assembly caninclude, in some cases, a wire or a rod disposed proximally of thetubular distal end and coaxially within the catheter lumen, in whichcase the release wire extends parallel to the pusher assembly, or thepusher can include a coiled segment disposed proximally of the tubulardistal end, in which case the release wire can be disposed coaxiallywithin a lumen defined by the coiled segment.

In yet another aspect, the present invention relates to a method oftreating a patient by inserting into that patient's body a catheterhaving a pusher assembly, distal receiving element, constraining elementand embolic coil with a bulbous element as described above. Onceinserted, at least one of the pusher assembly and the constrainingelement is moved relative to the other, thereby permitting the bulbouselement to separate from the distal receiving element. As above, in somecases the inner diameter of the tubular distal end of the constrainingelement is not more than 133% of the outer diameter of the bulbouselement of the embolic coil plus the thickness of the second portion ofthe distal receiving element, the protrusion extends a distance from theelongated planar surface that is less than 50% of a diameter of thebulbous element, and/or the combination of the extension of theprotrusion from the elongated planar surface and the second portion ofthe distal receiving element is greater than or equal to a differencebetween the inner diameter of the tubular distal end of the constrainingelement and the combined outer diameter of the bulbous element of theembolic coil and the second portion of the distal receiving element. Thebulbous element can be connected to the embolic coil by one of a wireand a rod extending axially along a central axis of the coil, such thatthe wire or rod extends axially along a central axis of the embolic coilwhen the bulbous element and receiving element are engaged and disposedwithin the lumen of the tubular distal end of the constraining element.The method can also include a step of retracting the pusher assembly,and may also include a step of retracting the constraining element priorto the retraction of the pusher assembly. In some cases, the pusherassembly and the constraining element are withdrawn from the catheter,and a pusher assembly and constraining element engaged with a bulbouselement of a second embolic coil is reinserted into the catheter.Finally, in some cases the method includes positioning at least part ofthe embolic coil within a vascular structure to be occluded.

DRAWINGS

Aspects of the invention are described below with reference to thefollowing drawings in which like numerals reference like elements, andwherein:

FIG. 1 shows a schematic view of a delivery catheter according tocertain embodiments of the present invention.

FIGS. 2A, 2B and 2C show schematic views of the catheter of FIG. 1 atthree points during the detachment process.

FIG. 3 shows a schematic depiction of a receiving element as used in thedelivery catheter of FIGS. 1 and 2.

FIGS. 4A, B, C, D, E and F show, in schematic form, various alternativeconfigurations of delivery catheters according to the embodiments of thepresent invention.

Unless otherwise provided in the following specification, the drawingsare not necessarily to scale, with emphasis being placed on illustrationof the principles of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An exemplary catheter assembly 100, as shown in FIG. 1, includes agenerally tubular catheter 105, an embolic coil 110 (though any otherimplantable medical device of similar size may be used) having, at itsproximal end, a ball or other bulbous element 111, a pusher assembly 115slidably disposed within the catheter 105 and having, at its distal end,a receiving element 116 that is sized to engage the ball 111. Thecatheter assembly 100 also includes a constraining element 120 that isslidable within the catheter lumen independently of the pusher assembly115 and which constrains the axial or radial movement of the ball 111when it is engaged with the receiving element 116.

The constraining element 120 depicted in FIGS. 1 and 2 has a generallytubular distal end and has an inner diameter that is slightly largerthan the combined width of the ball 111 and the receiving element 115when the two are engaged (e.g. 10% larger, 20% larger, 30% larger, 40%larger or 50% larger). Together with a lip or ridge 116 a on thereceiving element, the constraining element 120 helps limit both theaxial and radial movement of the ball 111 when it is engaged with thereceiving element 116 and is contained within the lumen of theconstraining element 120. This arrangement is shown in FIG. 2A and isused to advance the coil 110 through the distal end of the catheter 105.

As FIG. 2B illustrates, as the coil 110 is advanced through the distalend of the catheter 105, the constraining element 120 remains positionedover the ball 111 and the receiving element 116 of the pusher assembly115, permitting the placement of the coil 110 prior to its release. Whenrelease of the coil is desired, the constraining element 120 isretracted over the pusher assembly 115 or, alternatively, the pusherassembly 115 is advanced through the constraining element 120; in eithercase, the ball 111 is exposed (FIG. 2C), thereby releasing the emboliccoil 110.

The catheter assembly 100 shown in FIGS. 1 and 2 has severaladvantageous characteristics, including without limitation thefollowing: it is 100% detachable yet it allows a user to recapture thecoil 110 by engaging the receiving element 116 with the ball 111 andadvancing the constraining element 120 over both. At the same time, thesimple design has a small overall diameter that will tend to preservethe flexibility of the catheter assembly 100 and can be implementedusing materials that are currently used to produce delivery catheters.

Turning now to FIG. 3, an exemplary receiving element 116 includes aproximal axially constraining surface 116 b and a radially constrainingsurface 116 c which in turn includes, at its distal end, a ridge or lip116 a that serves to further limit the axial movement of the ball 111and therefore the coil 110 when the constraining element 120 is extendedover the ball 111 and the receiving element 116. Each of the proximalaxially constraining surface 116 b, the radially constraining surface116 c and the lip or ridge 116 a are generally continuous with oneanother (such that the receiving element 116 can be fabricated as asingle piece) and preferably have relatively flat (in the case of theradial and axial constraining surface), even surfaces.

The receiving element 116 depicted in FIG. 3 is superficially similar tothe design of Engelson disclosed in U.S. Pat. No. 5,261,916 (which isincorporated by reference in its entirety and for all purposes herein),but the skilled artisan will appreciate that Engelson utilizes a pusherwith an enlarged cylindrical tip having both an axial bore and a radialslot to receive the ball of the embolic coil, such that the coil isconstrained both proximally and distally by a body having a diameterequal to or greater than the diameter of the ball. In the embodiment ofFIGS. 1-3, however, the lip 116 a is significantly smaller than thediameter of the ball 111. For instance, in one case the ball 111 has adiameter of approximately 0.012″ (0.30 mm), while the lip or ridge 116 amay have a convex curved surface with a radius of 0.0035″ (0.09 mm).More generally, the lip 116 a preferably extends a distance that isequal to or, preferably, slightly greater than the difference betweenthe inner diameter of the constraining element 120 and the combinedouter diameters of the receiving element 116 and the ball 111 when thetwo are engaged. This configuration limits radial displacement of theball 111 and the proximal end of the embolic coil 110 during thedelivery process, aiding accurate placement of the coil 110 with arelatively low risk of coil movement during release. At the same time,the distance is not so great as to reduce the mechanical clearance ofthe ball 111 or the connector between the ball 111 and the coil 110 whenit is engaged with the receiving element 116 and the constrainingelement 120.

While the embodiments presented above exemplify certain aspects of thepresent invention, it is not limited in scope to those aspects. Forinstance, the constraining element 120 is depicted throughout FIGS. 1, 2and 3 as a cylindrical body having constant inner and outer diametersand extending the entire length of the catheter assembly 100. Thisarrangement has the advantages described above, but the resultingcatheter assembly 100 may be comparatively stiff, as the constrainingelement is preferably robust to deformation or “ovalization” that couldpotentially allow the ball 111 to migrate during delivery.

In situations where embolic coils are to be delivered through tortuousand/or narrow diameter vessels, a more flexible catheter may be desired;this is achieved in various embodiments by altering the diameter, lengthor rigidity of the constraining element 120 along the length of thecatheter assembly 100. For instance, in some cases, the diameter of theconstraining element 120 is maximized at its distal end so as toencompass the ball 111 and the receiving element 116, then decreasesproximally. Alternatively, the distal portion of the constrainingelement 120 may be made more rigid than the proximal portion (e.g. bymeans of greater wall thickness, incorporation of a rigid material suchas a reinforcing fiber or braid, or a rigid bushing) allowing the distalend to resist ovalization while the proximal end retains flexibility.And, in yet another alternative illustrated in FIGS. 4A-B, the distalconstraining element 120 has a length that is significantly less thanthe length of the catheter 105 and is connected, at its proximal end, toa wire or other structure 121 that enables the constraining element 120to be pushed or pulled relative to the catheter 105 and/or the pusherassembly 115. In the embodiments shown in FIGS. 1-3, the constrainingelement 120 and the pusher assembly are arranged coaxially (i.e. thepusher assembly 115 is centered) along substantially all of the lengthof the catheter assembly 100; in the embodiment of FIG. 4A, the wire 121is centered, and the constraining element includes an off-centerproximal aperture 122 to accommodate the pusher assembly 115.Alternatively, if the pusher assembly 115 is centered, the proximalaperture 122 is located more centrally, while the wire 121 is off-centeras shown in FIG. 4B.

In addition to improved flexibility, the relatively short constrainingelement 120 shown in FIGS. 4A-B, as well the embodiments describedbelow, facilitate of fluid injection through the delivery catheter 105:the use of a tubular constraining element 120 of relatively short lengthmay reduce the fluid pressure necessary to inject fluid through thecatheter 105, by providing a comparatively larger inner diameter acrossmost of its length. By contrast, the diameter of the lumen available forfluid flow is reduced along the entire length of the catheter 105 whenthe constraining element 120 is a tube extending the entire length ofthe catheter 105.

Embolic coil 110 will, in certain embodiments, have both a primaryhelical structure and a complex secondary structure, such as a helix, anovoid shape, a J-shape, etc., as described in U.S. Pat. No. 5,639,277 toMariant, et al, which is incorporated by reference herein for allpurposes. Because the coil 110 tends to assume the secondary shape whenunconstrained, it may expand while disposed within the lumen of thecatheter 105 and, as the coil 110 is advanced through the catheter 105,it may tend to twist. One potential complication of the designs of FIGS.4A-B, and those described below, is that this twisting may cause thewire 121 to twist, potentially twisting around the pusher assembly 115.In order to prevent twisting of the wire 121 and the pusher assembly115, the catheter optionally includes constraining elements such assmall bushings, or wire rings, which limit the circumferential and/orradial movement of one or both of the wire 121 and the pusher assembly115. These wires, bushings, etc. are preferably positioned at multipleplaces along the length of the catheter 105, thereby ensuring that thewire 121 and the pusher assembly 115 do not mechanically interfere withone another along the length of the catheter 105 during the deliveryprocess.

In another group of embodiments, a pusher assembly including a receivingelement provides both radial and axial constraint of the ball with theaid of a wire or other narrow body that urges the ball and the receivingelement together. For instance, in FIGS. 4C-D, a catheter assembly 400includes a catheter 405 for delivering an embolic coil 410 having aproximal ball 411, which catheter includes a pusher assembly 415 with atubular receiving element 416 having an axial bore defining a lumen anda slot 417 cut into the side-wall of the receiving element 416 that issized to accommodate part or all of the ball 111. The assembly alsoincludes a release wire 420 slidably disposed in the catheter 405 thatis independent of the pusher assembly 415. The release wire 420 ispositioned to urge the ball 411 toward the slot 417, providing axial andradial constraint of the ball 411 during delivery. As discussed above,either the pusher assembly 415 or the release wire 420 can be centered,in which case the other is off-center. In either case, the release wire420 and the pusher assembly 415 are optionally constrained to preventtangling or crossing at one or more points along the length of thecatheter 405, for instance by one or more wire rings, or by the use of aguidewire lumen or slit within the catheter 405 (not shown).

In use, the catheter assembly 400 operates by “pull release”: in orderto deploy the coil 410, the pusher assembly 415 and the release wire 420are advanced distally relative to the catheter 405; once the coil issuitably positioned, the release wire 420 is retracted proximally,thereby releasing the coil 410.

Turning now to FIGS. 4E-F, in some cases, the pusher assembly andconstraining element are arranged coaxially, with the pusher element 115being central and extending through a hollow central portion 130 of theconstraining element 120 (FIG. 4E). Alternatively, as shown in FIG. 4F,the release wire 420 can extend through a hollow central portion 430 ofthe pusher assembly 416. The hollow central portion 130 430 can be acoil or other suitable hollow body through which the pusher assembly 115or the release wire 420, respectively, is be slidably disposed.

The phrase “and/or,” as used herein should be understood to mean “eitheror both” of the elements so conjoined, i.e., elements that areconjunctively present in some cases and disjunctively present in othercases. Other elements may optionally be present other than the elementsspecifically identified by the “and/or” clause, whether related orunrelated to those elements specifically identified unless clearlyindicated to the contrary. Thus, as a non-limiting example, a referenceto “A and/or B,” when used in conjunction with open-ended language suchas “comprising” can refer, in one embodiment, to A without B (optionallyincluding elements other than B); in another embodiment, to B without A(optionally including elements other than A); in yet another embodiment,to both A and B (optionally including other elements); etc.

The term “consists essentially of” means excluding other materials thatcontribute to function, unless otherwise defined herein. Nonetheless,such other materials may be present, collectively or individually, intrace amounts.

As used in this specification, the term “substantially” or“approximately” means plus or minus 10% (e.g., by weight or by volume),and in some embodiments, plus or minus 5%. Reference throughout thisspecification to “one example,” “an example,” “one embodiment,” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the example is included inat least one example of the present technology. Thus, the occurrences ofthe phrases “in one example,” “in an example,” “one embodiment,” or “anembodiment” in various places throughout this specification are notnecessarily all referring to the same example. Furthermore, theparticular features, structures, routines, steps, or characteristics maybe combined in any suitable manner in one or more examples of thetechnology. The headings provided herein are for convenience only andare not intended to limit or interpret the scope or meaning of theclaimed technology.

Certain embodiments of the present invention have been described above.It is, however, expressly noted that the present invention is notlimited to those embodiments, but rather the intention is that additionsand modifications to what was expressly described herein are alsoincluded within the scope of the invention. Moreover, it is to beunderstood that the features of the various embodiments described hereinwere not mutually exclusive and can exist in various combinations andpermutations, even if such combinations or permutations were not madeexpress herein, without departing from the spirit and scope of theinvention. In fact, variations, modifications, and other implementationsof what was described herein will occur to those of ordinary skill inthe art without departing from the spirit and the scope of theinvention. As such, the invention is not to be defined only by thepreceding illustrative description.

What is claimed is:
 1. A system for treating a patient, comprising: acatheter defining a lumen: a pusher assembly slidably disposed withinthe lumen; a constraining element slidably disposed within the lumen andmoveable independently of the pusher assembly, the constraining elementhaving a tubular distal end disposable about a distal portion of thepusher assembly; and an embolic coil with a proximal end comprising abulbous element; wherein the pusher assembly includes a distal receivingelement having a first portion defining a first planar surface extendingradially and a second portion defining an elongated planar surfaceextending substantially perpendicular to and distally from the firstplanar surface, the elongated planar surface having a protrusionextending away from the elongated planar surface; wherein the firstplanar surface, the elongated planar surface, and the protrusion areconfigured to accept at least a portion of the bulbous element; andwherein the protrusion extends a distance from the elongated planarsurface that is less than 50% of a diameter of the bulbous element. 2.The system according to claim 1, wherein an inner diameter of thetubular distal end of the constraining element is not more than 133% of(a) an outer diameter of the bulbous element of the embolic coil plus(b) a thickness of the second portion of the distal receiving element.3. The system according to claim 1, wherein a combined thickness of theprotrusion from the elongated planar surface and the second portion ofthe distal receiving element is greater than or equal to a differencebetween the inner diameter of the tubular distal end of the constrainingelement and a combined thickness of an outer diameter of the bulbouselement of the embolic coil and the second portion of the distalreceiving element.
 4. The system according to claim 1, wherein thebulbous element is connected to the embolic coil by one of a wire and arod extending axially along a central axis of the coil, and wherein thewire or rod extends axially along a central axis of the embolic coilwhen the bulbous element and receiving element are engaged and disposedwithin the lumen of the tubular distal end of the constraining element.5. The system of claim 1, wherein the constraining element includes awire or a rod disposed proximally of the tubular distal end, the wire orrod extending parallel to the pusher assembly, and wherein the pusherassembly is disposed coaxially within the catheter lumen.
 6. The systemof claim 1, wherein the constraining element includes a coiled segmentdisposed proximally of the tubular distal end, and wherein the pusherassembly is disposed coaxially within a lumen defined by the coiledsegment.
 7. The system of claim 1, wherein the constraining elementincludes a wire or a rod disposed proximally of the tubular distal endand disposed coaxially within the catheter lumen, the pusher assemblyincludes an elongated portion extending parallel to the wire and througha proximal aperture within the tubular distal end.
 8. A method oftreating a patient, comprising the steps of: inserting, into the body ofthe patient, a catheter defining a lumen and having, slidably disposedwithin the lumen: a pusher assembly including a distal receiving elementhaving a first portion defining a first planar surface extendingradially and a second portion defining an elongated planar surfaceextending substantially perpendicular to and distally from the firstplanar surface, the elongated planar surface having a protrusionextending away from the elongated planar surface; a constraining elementslidably disposed moveable independently of the pusher assembly, theconstraining element having a tubular distal end disposable about thedistal receiving element; and an embolic coil with a proximal endcomprising a bulbous element engaged with the distal receiving elementand the constraining element; wherein the protrusion extends a distancefrom the elongated planar surface that is less than 50% of a diameter ofthe bulbous element; and moving at least one of the pusher assembly andthe constraining element relative to the other, thereby permitting thebulbous element to separate from the distal receiving element.
 9. Themethod of claim 8, wherein an inner diameter of the tubular distal endof the constraining element is not more than 133% of (a) an outerdiameter of the bulbous element of the embolic coil, plus (b) athickness of the second portion of the distal receiving element.
 10. Themethod of claim 8, wherein a combined thickness of the protrusion fromthe elongated planar surface and the second portion of the distalreceiving element is greater than or equal to a difference between theinner diameter of the tubular distal end of the constraining element anda combined thickness of an outer diameter of the bulbous element of theembolic coil and the second portion of the distal receiving element. 11.The method of claim 8, wherein the bulbous element is connected to theembolic coil by one of a wire and a rod extending axially along acentral axis of the coil, and wherein the wire or rod extends axiallyalong a central axis of the embolic coil when the bulbous element andreceiving element are engaged and disposed within the lumen of thetubular distal end of the constraining element.
 12. The method of claim8, further comprising the step of retracting the pusher assembly. 13.The method of claim 12, wherein the constraining element is retractedprior to the pusher assembly.
 14. The method of claim 8, wherein thepusher assembly and the constraining element are withdrawn from thecatheter, and an assembly and constraining element engaged with abulbous element of a second embolic coil is reinserted into thecatheter.
 15. The method of claim 8, further comprising positioning atleast part of the embolic coil within a vascular structure to beoccluded.